Method for protection switching in ethernet ring network

ABSTRACT

Provided is a protection switching method via forwarding table correction in an Ethernet ring network. Upon detecting a failure in a link, a node generates a protection switching frame including an address list of a forwarding table corresponding to a port connected to the link, and transmits the protection switching frame to a port at an opposite direction of the link. A node that receives the protection switching frame deletes its own address from the address list included in the protection switching frame, and changes a port number of an address in the address list of the protection switching frame from among addresses of the forwarding table corresponding to a port that received the protection switching frame to a port number in an opposite direction of the port that received the protection switching frame or deletes the port number of the address in the address list.

TECHNICAL FIELD

The present invention relates to a protection switching method in anEthernet ring network, and more particularly, to a protection switchingmethod via transmission table correction of an Ethernet ring node.

The present invention is derived from a research project supported bythe Information Technology (IT) Research & Development (R&D) program ofthe Ministry of Information and Communication (MIC) and the Institutefor Information Technology Advancement (IITA) [2005-S-102-03, CarrierClass Ethernet Technology].

BACKGROUND ART

In order to provide Ethernet ring protection switching, a forwardingtable is prepared so that frame forwarding of each Ethernet node doesnot form an endless loop in an Ethernet ring. Such forwarding table isrealized via a link blocking method and an active management method.

According to the link blocking method, a link included in a ring isdeactivated so as to logically prevent the ring from forming as if thelink does not exist, and endless loop transmission is prevented bypreparing a forwarding table of each node by using an address learningmethod used in a general Ethernet media access control (MAC). Here, ablock link is only logically determined, and a physical link of theblock link exists. Thus, when such local block link is removed,transmission of traffic is immediately possible.

According to the active management method, a manager or a routingprotocol manages contents of the forwarding table of each node, orendless loop transmission is prevented by combining the activemanagement method and the address learning method. The active managementmethod is highly efficient since the optimum path is provided via aneffective forwarding table.

When a failure occurs in a conventional Ethernet ring network, a blocklink is removed if the block link logically exists in a ring, andendless loop transmission of the ring is prevented as a failure linkprovides a physical or logical block. When several Ethernet rings arecombined, a block link of a ring where a failure is not occurred isnewly selected so that the whole Ethernet network forms a spanning treestructure without a loop.

When a physical block link due to a failure and a block link for loopprevention are newly selected, a forwarding table is no longer valid,and thus all nodes require new forwarding tables. In order to prepare anew forwarding table, all nodes start a new address learning process.During the address learning process, a node, which received a frameincluding a destination address (DA) that is not yet learned, broadcaststhe frame through all ports. Then, if a source address (SA) of a frameis not learned in the forwarding table, the SA of the frame and a portnumber that received the frame are recorded in the forwarding table. Inother words, forwarding tables are all removed after protectionswitching, and thus whenever a frame having a new address that is notrecorded in the forwarding table as a DA is received, the frame iscopied and transmitted towards the both direction of a ring.Accordingly, the larger amount of frames than a normal state is providedin the Ethernet ring network until all SAs are learned.

In other words, since a protection switching technology in aconventional ring network deletes and initiates forwarding tableinformation, a transition phenomenon occurs, where the amount of trafficovershoots after protection switching. In order to prevent a packet lossdue to such transmission phenomenon, the link amount of the ring networkor the bandwidth of the ring network should be obtained more thannecessary, which is inefficient.

When the link amount or the bandwidth of the ring network is limited, alarge capacity buffer may be used in order to prevent the packet loss.However in this case, prompt protection switching (protection switchingwithin 50 ms generally required in a real time voice communicationcentered network) cannot be provided.

DETAILED DESCRIPTION OF THE INVENTION Technical Problem

The present invention provides a protection switching method whichsolves a problem of an ineffective protection switching technology in anEthernet ring network, and settles a transition phenomenon where thetraffic amount overshoots after protection switching.

The present invention also provides an effective protection switchingmethod which uses a share node in an Ethernet multi-ring network.

Technical Solution

According to an aspect of the present invention, there is provided aprotection switching method of a node connected to a link having afailure in a ring network, the protection switching method including:generating a protection switching frame including an address list of aforwarding table corresponding to a port connected to the link; andtransmitting the protection switching frame.

According to another aspect of the present invention, there is provideda protection switching method of a node receiving a protection switchingframe in a ring network, the protection switching method including:receiving the protection switching frame; deleting an address of thenode from an address list included in the protection switching frame;and correcting a port number of an address included in the address listfrom among addresses of a forwarding table of the node corresponding toa port that received the protection switching frame to a port number atan opposite direction of the port that received the protection switchingframe.

According to another aspect of the present invention, there is provideda protection switching method of a node receiving a protection switchingframe in a ring network, the protection switching method including:receiving the protection switching frame; deleting an address of thenode from an address list included in the protection switching frame;and deleting a port number of an address included in the address listfrom among addresses of a forwarding table of the node corresponding toa port that received the protection switching frame to a port number atan opposite direction of the port that received the protection switchingframe.

According to another aspect of the present invention, there is provideda protection switching method of a node receiving a protection switchingframe in a ring network, the protection switching method including:receiving the protection switching frame; deleting an address of thenode from an address list included in the protection switching frame;and deleting an address of the forwarding table of the nodecorresponding to a port connected to an external network of the ringnetwork, from the address list of the protection switching frame.

According to another aspect of the present invention, there is provideda protection switching method of a node receiving a protection switchingframe in a ring network, the protection switching method including:receiving the protection switching frame; deleting an address of thenode from an address list included in the protection switching frame;and discarding the protection switching frame when an address no longerexists in the address list.

According to another aspect of the present invention, there is provideda to protection switching method of a share node connected to a sharelink having a failure in a multi-ring network, the protection switchingmethod including: generating a protection switching frame for each ring;and transmitting the protection switching frame to the each ring,wherein the protection switching frame comprises from among addresses ofa forwarding table of the share node: an address corresponding to a portconnected to the share link while belonging to a ring that is totransmit the protection switching frame; and an address corresponding toa blocked port in a neighboring ring direction while belonging to aneighboring ring instead of the ring that is to transmit the protectionswitching frame.

Advantageous Effects

According to the present invention, quick protection switching isprovided in an Ethernet ring network, and an overshoot transitionphenomenon that occurs after the protection switching is reduced byusing a protection switching frame that does not require large bandwidthand is effective. Also, by reducing a network bandwidth and unnecessaryusage of a buffer, resources and expenses can be reduced.

Also, by using a block bridge using first and second share nodes in anEthernet multi-ring network, protection switching within 50 ms can beeffectively provided without a conventional overshoot transitionphenomenon.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a protection switching method in a ringtopology using a block link method according to an embodiment of thepresent invention;

FIG. 2 is a diagram illustrating a protection switching method in a ringtopology using an active management method according to an embodiment ofthe present invention;

FIG. 3 is a diagram illustrating a protection switching method when aone-way direction failure occurs in a ring topology using an activemanagement method according to an embodiment of the present invention;

FIG. 4 is a flowchart illustrating a process of transmitting aprotection switching frame according to an embodiment of the presentinvention;

FIG. 5 is a flowchart illustrating a protection switching process of anode that received a protection switching frame according to anembodiment of the present invention;

FIG. 6 is a flowchart illustrating a method of deleting port assignmentof a forwarding table of each node in a protection switching node,according to an embodiment of the present invention;

FIGS. 7 through 12 are diagrams illustrating a protection switchingmethod according to an embodiment of the present invention when anEthernet ring is formed with an optimized forwarding table that preventsa loop without a block link;

FIG. 13 is a diagram illustrating a protection switching methodaccording to an embodiment of the present invention when one share nodeexists in an Ethernet multi-ring network;

FIGS. 14 through 15 are diagrams illustrating a protection switchingmethod according to an embodiment of the present invention when twoshare nodes exist in an Ethernet multi-ring network;

FIGS. 16 through 17 are diagrams illustrating a protection switchingmethod according to an embodiment of the present invention when at leastthree share node exist in an Ethernet multi-ring network;

FIG. 18 is a flowchart illustrating a method of transmitting aprotection switching frame when a failure occurs in an Ethernetmulti-ring network according to an embodiment of the present invention;and

FIG. 19 is a flowchart illustrating a protection switching method of anode that received a protection switching frame when a failure occurs inan Ethernet multi-ring network.

MODE OF THE INVENTION

The present invention will now be described more fully with reference tothe accompanying drawings, in which exemplary embodiments of theinvention are shown.

An Ethernet ring network is formed of Ethernet nodes. An Ethernet nodeincludes a plurality of Ethernet ports. At least two Ethernet ports ofeach Ethernet node are connected to a link that is connected to aneighbouring Ethernet node so as to form a ring. Other Ethernet portsare connected to an Ethernet network outside the Ethernet ring network.

The Ethernet ring network may have a physical ring form, or a logicalring form in a predetermined network that is physically connected. Alogical ring may be formed of a ring that uses a block link and a ringthat does not use a block link. The present invention provides aprotection switching method that can be commonly used in both rings.

A protection switching method of an Ethernet ring network according tothe present invention will now be described with reference to theaccompanying drawings.

FIG. 1 is a diagram illustrating a protection switching method in a ringtopology using a block link method according to an embodiment of thepresent invention.

According to a method of deactivating a link, a port of any one nodefrom among nodes at both ends of the link may be blocked or all ports ofthe nodes at the both ends of the link may be blocked.

In FIG. 1, a block link 110 between nodes C and D are logically blocked.In this case, each node of a network 100 is physically connected like aring, but logically connected in a tree form. Also, each node includes aforwarding table, for example, a filtering database (FDB), and adestination address of a packet is determined by using the forwardingtable, i.e. to which port the packet is to be transmitted.

When a failure occurs in a failure link 120 between nodes A and B, thenodes A and B, upon detecting the failure, transmit an automaticprotection switching (APS) frame to a link in an opposite direction ofthe failure link 120. Accordingly, a block of the block link 110 betweenthe nodes C and D is removed, and the block link 110 is activated. Atthis time, the nodes A and B change a port number of all addresses of aforwarding table corresponding to a port connected to the failure link120 to a port number connected to the link in the opposite direction ofthe failure link 120 so that a frame is not transmitted to the failurelink 120. Simultaneously, the nodes A and B load an address list of theforwarding table corresponding to the port connected to the failure link120 on a payload of the protection switching frame. In other words, thenode A loads an address list of a forwarding table having a port numberconnected to the failure link 120, i.e. media access control (MAC)addresses of the nodes B and C, on the payload of the protectionswitching frame. A structure of the protection switching frameillustrated in FIG. 1 includes a field indicating multicasttransmission, a destination address field, and a payload.

A node that received the protection switching frame determines whetherits own MAC address is included in the address list loaded on thepayload of the protection switching frame, and if the MAC address isincluded, the MAC address is deleted from the address list. For example,when the node C receives a protection switching frame generated in thenode A, the node C deletes its own MAC address C from an address list(B, C) included in the protection switching frame, and then transmitsthe protection switching frame to the node D.

Also, the node that received the protection switching frame determineswhether an address to which a port connected to an external network isassigned exists in the address list of the protection switching frame,and if the address exists, the address is deleted from the address listof the protection switching frame. Also, the node recognizes addresses,to which a port that received the protection switching frame isassigned, from the forwarding table, and changes a port numbercorresponding to an address in the address list of the protectionswitching frame from among the recognized addresses to a port number inan opposite direction of the port that received the protection switchingframe or deletes the port number corresponding to the address in theaddress list. After all nodes performed above processes, the correctedforwarding table of each node provides protection switching thattransmits a packet without using the failure link 120.

FIG. 2 is a diagram illustrating a protection switching method in a ringtopology using an active management method according to an embodiment ofthe present invention.

Referring to FIG. 2, the active management method uses all links withouta block link. When a failure occurs in a link 100 between nodes C and D,the nodes C and D detect the failure. Upon detecting the failure, thenodes C and D recognize an address list, which transmits a packet to aport in a direction where the failure occurred, from a forwarding table,and changes a port number corresponding to an address in the recognizedaddress list to a port number in an opposite direction of the failure sothat the packet is transmitted to the opposite direction.

Also, the nodes C and D, upon detecting the failure, each generates aprotection switching frame including the address list whose port numbersare changed in the forwarding table, and transmits the protectionswitching frame to an opposite direction of the port with the failure.In other words, the protection switching frame loads the address list ofthe forwarding table where the link or the port with the failure isassigned. The nodes C and D multicast the protection switching frame.

Upon receiving the protection switching frame, another node excludingthe node that detected the failure updates its own forwarding table byperforming the same operation as described in FIG. 1. In other words,the another node deletes its own address and an address assigned to anexternal port of itself from the address list loaded on the protectionswitching frame.

A normal node in a non-failure state receives two protection switchingframes each generated in two nodes at the both ends of a failure link.If the normal node does not delete its own address or the like fromaddress lists of the protection switching frames, corrections in aforwarding table of the normal node made by the pre-received protectionswitching frame may be changed again by the post-received protectionswitching frame. In other words, if the address of the already passednode and an address of an external node connected to the node are leftin the address list of the post-received protection switching frame, thecorrections in the forwarding table of the node corrected by thepre-received protection switching frame may be changed again by thepost-received protection switching frame. In order to prevent suchphenomenon, the address of a node that received the protection switchingframe and the address of an external node connected to the node shouldbe deleted from the address list loaded on the payload of the protectionswitching frame.

Also, when an address of a forwarding table to which a port thatreceived the protection switching frame is assigned is included in theaddress list loaded in the protection switching frame, a port number ofsuch address is changed to a port number in an opposite direction of theport that received the protection switching frame or deleted from theforwarding table.

FIG. 3 is a diagram illustrating a protection switching method when aone-way direction failure occurs in a ring topology using an activemanagement method according to an embodiment of the present invention.

Referring to FIG. 3, when a failure occurs in a link from a node C to anode D, the node D cannot receive a continuity check (CC) frame from thenode C, and thus transmits a remote defect indication (RDI) frame to thenode C. Upon receiving the RDI frame, the node C multicasts a protectionswitching frame to an opposite direction of receiving the RDI frame.Here, the protection switching frame includes an MAC address list of aforwarding table corresponding to a port that is outputted to the linkfrom the node C to the node D. Operations of a node that received theprotection switching frame are equal to those described with referenceto FIG. 1, and thus detailed descriptions thereof will be omitted.

When the node C receives the protection switching frame, since adestination address of the protection switching frame and the address ofthe node C are the same, the protection switching frame is discarded. Inthis manner, the protection switching frame is transmitted to onedirection when the one-way failure occurs so as to perform a protectionswitching function.

FIG. 4 is a flowchart illustrating a process of transmitting aprotection switching frame according to an embodiment of the presentinvention.

Referring to FIG. 4, nodes located at both ends of a link periodicallytransceives a CC frame in operation S400. Upon receiving the CC frame,the node initiates a CC frame reception timer. If the CC frame is notreceived until the CC frame reception timer expires in operation S410,the node determines that a failure occurred in a link that did notreceive the CC frame, and blocks a port connected to the link with thefailure in operation S420. A port number of addresses of a forwardingtable corresponding to the blocked port is changed to a port number inan opposite direction of the link with the failure in operation S430.Then, then node transmits a protection switching frame including anaddress list of the forwarding table whose port numbers are changed to alink at an opposite direction of the failure in operation S440.

FIG. 5 is a flowchart illustrating a protection switching process of anode that received a protection switching frame according to anembodiment of the present invention.

Referring to FIG. 5, a node of an Ethernet ring that received aprotection switching frame generated by a node with a failure determineswhether its own MAC address is included in an address list loaded on apayload of the protection switching frame in operation S500. If its ownMAC address is included in the address list, the node deletes the MACaddress from the address list in operation S510. If an address assignedto a port connected to an external ring in the forwarding table of thenode exists in the address list of the protection switching frame inoperation S520, the node deletes such address from the address list inoperation S530.

After such deleting processes, the node discards the protectionswitching frame if the address list does not exist in the payload of theprotection switching frame. If an address is left in the payload, thenode determines whether a same address exists by comparing an addresslist in its own forwarding table and the address list in the payload inoperation S540. If the same address exists, a port number correspondingto the same address in the forwarding table is changed to an oppositeport number of a logical ring formed of a virtual local area network(VLAN) in operation S550, and the protection switching frame istransmitted to a next ring node in operation S560. When each node of theEthernet ring performs the protection switching process, a forwardingtable providing a protection switching function is prepared.

FIG. 6 is a flowchart illustrating a method of deleting port assignmentof a forwarding table of each node in a protection switching node,according to an embodiment of the present invention.

Referring to FIG. 6, upon receiving a protection switching frame, a nodedeletes its own MAC address and an address assigned to an external portfrom an address list loaded on a payload of the protection switchingframe in operations S600, S610, S620, and S630. As operations S600,S610, S620, and 5630 are equal to operations S500, S510, S520, and S530of FIG. 5, detailed descriptions thereof are omitted herein. After suchdeleting processes, the node determines whether a same address exists bycomparing an address list of a forwarding table and the address list ofthe protection switching frame in operation S640. Then, the node deletesthe same address from the forwarding table in operation S650, andtransmits the protection switching frame to a next ring node inoperation S660. The method uses a characteristic of broadcasting a framein a VLAN when a destination address is not in a forwarding table in anEthernet MAC. According to the method, a protection switching frame canbe quickly provided by reducing time consumed in correcting a forwardingtable in one node.

FIGS. 7 through 12 are diagrams illustrating a protection switchingmethod according to an embodiment of the present invention when anEthernet ring is formed with an optimized forwarding table that preventsa loop without a block link.

Referring to FIGS. 7 through 12, all nodes in the Ethernet ringperiodically transceives a CC frame with neighboring nodes. When afailure occurs in a link between nodes A and B, a CC frame receptiontimer of the nodes A and B expires, and the link between the nodes A andB physically becomes a block link. In this case, the nodes A and Bdetect the failure in the link, and transmit a protection switchingframe to a port at an opposite direction of the failure. Here, MACaddress information corresponding to a port 1 of the node A is includedin the protection switching frame transmitted by the node A, and MACaddress information corresponding to a port 12 of the node B is includedin the protection switching frame transmitted by the node B.

Each of nodes C, D, and E receives the protection switching frame,deletes its own MAC address from an MAC address list of the receivedprotection switching frame, and changes an MAC address overlapping withthe forwarding table of the port that received the protection switchingframe from among the left MAC addresses to a forwarding table of anopposite port of the node. Then, the protection switching frame istransmitted to a next node. When the forwarding tables of all nodes thatreceived the protection switching frame are changed, a protectionswitching function is provided, and remaining links excluding the linkwith the failure are used.

In the above, a protection switching method in a single Ethernet ringnetwork is described. Hereinafter, a protection switching method in anEthernet multi-ring network, wherein at least one ring is overlapped, isdescribed.

Multi-rings are connected by at least one share node and a share linkbetween share nodes. Each ring includes at least one block port or ablock link so as to prevent an endless loop from occurring. When afailure occurs in the share link and the block port or the lock link isremoved, one big ring wherein two rings are combined is formed, and thusany one bridge that connects the two rings from the bridges of the sharenodes should be blocked so as to prevent an endless loop in the bigring.

In order to classify each ring in the Ethernet multi-ring network, aVLAN identification (ID) is assigned to each ring. Accordingly, eachnode can determine whether a ring exists in the same ring or a differentring in the multi-ring network based on the VLAN ID included in a headerof a received packet. Specifically, a VLAN ID field is included in aforwarding table of the share node. Alternatively, when the multi-ringnetwork is a general network, each ring is classified by a virtualprivate network (VPN) assigned number. When the multi-ring network is alabel switching network, each ring may be classified by a multicastlabel. In addition, based on a type of the multi-ring network, variousidentifications may be used according to the corresponding type.

FIG. 13 is a diagram illustrating a protection switching methodaccording to an embodiment of the present invention when one share nodeexists in an Ethernet multi-ring network.

Referring to FIG. 13, the multi-ring network includes one share node,and does not have a share link. In order to prevent an endless loop,each ring of the multi-ring network includes a block port or a blocklink. Accordingly, in a standpoint of one ring, another ring is anexternal network of the share node. Thus in case of the multi-ringnetwork including one share node, the protection switching methoddescribed with reference to FIGS. 1 through 12 can be applied.

FIGS. 14 through 15 are diagrams illustrating a protection switchingmethod according to an embodiment of the present invention when twoshare nodes exist in an Ethernet multi-ring network. FIG. 14 illustratesa forwarding table of each node before protection switching and FIG. 15illustrates a forwarding table of each node after the protectionswitching.

Referring to FIGS. 14 and 15, each of two rings includes four nodes,where two nodes B and C are share nodes that connect the two rings. Inother words, a first ring network is formed of nodes A, B, C, and D, anda second ring network is formed of nodes B, C, E, and F. A node X is asubordinate network of the first ring network, and a node Y is asubordinate network of the second ring network. A subordinate networkmay be another ring network like FIG. 13. Hereinafter, it is assumedthat a port 11 of the node A and a port 5 of the port E are assigned asblock ports for preventing loop occurrence, and the forwarding table ofeach node is generated via a conventional MAC learning process. Also, Mis assigned as a VLAN ID in the first ring network, and N is assigned asa VLAN ID in the second ring network.

When a failure occurs in a share link between the share nodes B and C,the share nodes B and C respectively block ports 2 and 3 connected tothe share link, and the nodes A and E removes a previous block port.Accordingly, since two rings form one big ring, the share nodes B or Cshould block a bridge that connects the two rings so as to prevent theloop occurrence. In the current embodiment, the share node C blocks thebridge.

The share nodes B and C each transmit a protection switching frame to aring. The share nodes B and C each generate the protection switchingframe including an address corresponding to a blocked port number fromamong addresses of the forwarding table of a ring that receives theprotection switching frame from a share node, and an addresscorresponding to a blocked port number in a neighboring ring from amongaddresses of a forwarding table of the neighboring ring instead of thering that receives the protection switching frame from a share node.

For example, when the protection switching frame is transmitted to thefirst ring network, the share node B recognizes destination addresses A,C, D, and X of the nodes of the first ring network from the forwardingtable based on the VLAN ID (M), generates the protection switching frameincluding the addresses C, D, and X having the blocked port 2, andtransmits the protection switching frame to the first ring network. Theprotection switching frame is generated in the same manner when theshare node B transmits the protection switching frame to the second ringnetwork.

Alternatively, when the share node C that includes a bridge blocktransmits a protection switching frame to the first ring network, theshare node B recognizes addresses A, B, D, and X of the nodes of thefirst ring network from the forwarding table based on the VLAN ID (M),and recognizes the addresses A and B including the blocked port 3 in thefirst ring network. The share node C recognizes addresses B, E, F, and Yof nodes of the second ring network from the forwarding table based onthe VLAN ID (N), and recognizes the addresses E, F, and Y including theblocked port 32 in the second ring network whose bridge is blocked.Then, the share node C transmits the protection switching frameincluding the recognized addresses A, B, E, F, and Y to the first ringnetwork. The share node C generates the protection switching node in thesame manner even when the protection switching frame is to betransmitted to the second ring network.

The share nodes B and C each change a blocked port number in theforwarding table to a port number in an opposite direction of thefailure. The share nodes B and C include two ports in an oppositedirection of the share link, i.e. one port each that faces each ring.Accordingly, the share nodes B and C recognize to which ring an address,whose port number is to be changed in the forwarding table, belongs, andchange the address to the a port number of the corresponding ring.

For example, the share node B changes a port number of the addresses C,D, and X having the block port 2 from among the addresses A, C, D, and Xthat belongs to the first ring network whose VLAN ID is M in theforwarding table to a port 21 in the opposite direction. Also, the sharenode B changes a port number of the addresses E, F, and Y having theblock port 2 from among the addresses C, E, F, and Y that belongs to thesecond ring network whose VLAN ID is N to a port 22. Here, since theport number of the address C is already changed, it is not required tobe changed again. However, the port number of the address C may bechanged again. The forwarding table of the share node C is updatedaccording to the same manner.

FIGS. 16 through 17 are diagrams illustrating a protection switchingmethod according to an embodiment of the present invention when at leastthree share node exist in an Ethernet multi-ring network. FIG. 16illustrates a forwarding table before protection switching and FIG. 17illustrates a forwarding table after the protection switching.

Referring to FIGS. 16 and 17, the multi-ring network includes threeshare nodes A, B, and C, and two share links between the share nodes Aand B and the share nodes B and C. A node X is a subordinate network ofa first ring network and a node Y is a subordinate network of a secondring network. It is assumed that a port 14 of a node D and a port 6 of anode F are assigned as a block port for preventing loop occurrence, anda forwarding table of each node is generated via a conventional MAClearning process. Also, M is assigned as a VLAN ID in the first ringnetwork, and N is assigned as a VLAN ID in the second ring network.

When a failure occurs in the share link between the share nodes A and B,the share node A, upon detecting the failure, assigns a port 21 as ablock port, and a bridge connecting two rings as a block bridge. Also,the share node B, upon detecting the failure, blocks a port 2. The sharenodes A and B generates and transmits a protection switching frame inthe same manner as described with reference to FIGS. 14 and 15. Theshare node B inserts the VLAN ID in a header of the protection switchingframe so that the protection switching frame is transmitted only withinone ring. If a failure occurs in the share link between the share nodesB and C, the share node A cannot detect the failure, and thus the sharenode C generates a block bridge.

FIG. 18 is a flowchart illustrating a method of transmitting aprotection switching frame when a failure occurs in an Ethernetmulti-ring network according to an embodiment of the present invention.

Referring to FIG. 18, all nodes periodically transmit a CC frame inoperation S1100, and if the CC frame is not received within apredetermined time i.e. when a CC frame reception timer expires inoperation S1105, it is assumed that a failure occurred in a link.

In operation S1110, it is determined whether a node that detected thefailure is a share node or a general node in the multi-ring network. Ifthe node that detected the failure is a general node, the node blocks aport connected to the link having the failure in operation S1165,changes a port number of the blocked port to a port number in anopposite direction of the failure in a forwarding table in operationS1170, generates a protection switching frame including addresses of theforwarding table whose port number is changed in operation S1175, andtransmits the protection switching frame to the port in the oppositedirection of the failure in operation S1145.

If it is determined that the node that detected the failure is a sharenode in operation S1110, the node determines whether the defected linkis a share link or a general link in operation S1115. If the defectedlink is the general link, the share node blocks a port in a direction ofthe defected link in operation S1130, changes a port number of addressescorresponding to the blocked port to a port number in the oppositedirection of the failure in the forwarding table in operation S1135,generates a protection switching frame including an address list of theaddresses whose port number is changed in operation S1140, and transmitsthe protection switching frame to the port in the opposite direction ofthe failure in operation S1145. Since the protection switching frameincludes a VLAN ID indicating each ring in the multi-ring network, theprotection switching frame is transmitted within only one ring.

If it is determined that the node that detected the failure is the sharenode in operation S1110 and that the defected link is a share link inoperation S1115, the share node blocks a bridge connecting two rings inoperation S1150 so as to prevent a loop phenomenon in one big ringnetwork formed by two connected ring networks. When two share nodesexist as in FIG. 9A, a bridge of only one share node may be blocked.Then, the share node changes a port number of addresses corresponding tothe blocked port to a port number in the opposite direction of thefailure in the forwarding m table including the VLAN ID in operationS1155, generates a protection switching frame for each ring in operationS1160, and transmits the protection switching frame to the port in theopposite direction of the failure in operation S1145. The updating ofthe forwarding table of the share node and the generating of theprotection switching frame have been described above with reference toFIGS. 9A and 9B.

FIG. 19 is a flowchart illustrating a protection switching method of anode that received a protection switching frame when a failure occurs inan Ethernet multi-ring network.

Referring to FIG. 19, when a general node, instead of a share node,receives a protection switching frame in the multi-ring network, thegeneral node compares its own address with an address list included in apay load of the protection switching frame in operation S1205. If itsown address is included in the address list, the general node deletesits own address from the address list in operation S1210. Then, when itis determined that an address of a forwarding table assigned to a portfacing towards a subordinate network is included in the address list ofthe protection switching frame in operation S1220, the general nodedeletes the address of the forwarding table assigned to the port facingtowards the subordinate network from the address list in operationS1230. For example in FIG. 14, if an address of a forwarding tableassigned with a port connected to the subordinate network X is includedin the address list of the protection switching frame, the address isdeleted from the address list.

Then, if it is determined that an address of the forwarding tablecorresponding to a port that received the protection switching frame isincluded in the address list in operation S1240, the general nodechanges a port number of the address to a port number in an oppositedirection of the port that received the protection switching frame inoperation S1250. Then, the general node multicasts the protectionswitching frame to a next ring node in operation S1260.

The invention can also be embodied as computer readable codes on acomputer readable recording medium. The computer readable recordingmedium is any data storage device that can store data which can bethereafter read by a computer system. Examples of the computer readablerecording medium include read-only memory (ROM), random-access memory(RAM), CD-ROMs, magnetic tapes, floppy disks, optical data storagedevices, and carrier waves (such as data transmission through theInternet). The computer readable recording medium can also bedistributed over network coupled computer systems so that the computerreadable code is stored and executed in a distributed fashion.

While this invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention as defined by the appended claims. The preferred embodimentsshould be considered in descriptive sense only and not for purposes oflimitation. Therefore, the scope of the invention is defined not by thedetailed description of the invention but by the appended claims, andall differences within the scope will be construed as being included inthe present invention.

1. A protection switching method of a node connected to a link having afailure in a ring network, the protection switching method comprising:generating a protection switching frame including an address list of aforwarding table corresponding to a port connected to the link; andtransmitting the protection switching frame.
 2. The protection switchingmethod of claim 1, wherein the transmitting comprises transmitting theprotection switching frame to a port at an opposite direction of thelink.
 3. The protection switching method of claim 1, further comprisingcorrecting a port number of addresses of the forwarding tablecorresponding to the port connected to the link to a port number at theopposite direction of the link.
 4. The protection switching method ofclaim 1, wherein the detecting of the failure comprises: periodicallytransceiving a continuity check frame with neighboring nodes; initiatinga timer when the continuity check frame is received; and detecting afailure of a link that receives the continuity check frame, when thecontinuity check frame is not received until the timer expires.
 5. Aprotection switching method of a node receiving a protection switchingframe in a ring network, the protection switching method comprising:receiving the protection switching frame; deleting an address of thenode from an address list included in the protection switching frame;and correcting a port number of an address included in the address listfrom among addresses of a forwarding table of the node corresponding toa port that received the protection switching frame to a port number atan opposite direction of the port that received the protection switchingframe.
 6. The protection switching method of claim 5, further comprisingdeleting an address of the forwarding table of the node corresponding toa port connected to an external network of the ring network, from theaddress list of the protection switching frame.
 7. The protectionswitching method of claim 5, further comprising discarding theprotection switching frame when an address no longer exists in theaddress list.
 8. A protection switching method of a node receiving aprotection switching frame in a ring network, the protection switchingmethod comprising: receiving the protection switching frame; deleting anaddress of the node from an address list included in the protectionswitching frame; and deleting a port number of an address included inthe address list from among addresses of a forwarding table of the nodecorresponding to a port that received the protection switching frame toa port number at an opposite direction of the port that received theprotection switching frame.
 9. A protection switching method of a nodereceiving a protection switching frame in a ring network, the protectionswitching method comprising: receiving the protection switching frame;deleting an address of the node from an address list included in theprotection switching frame; and deleting an address of the forwardingtable of the node corresponding to a port connected to an externalnetwork of the ring network, from the address list of the protectionswitching frame.
 10. A protection switching method of a node receiving aprotection switching frame in a ring network, the protection switchingmethod comprising: receiving the protection switching frame; deleting anaddress of the node from an address list included in the protectionswitching frame; and discarding the protection switching frame when anaddress no longer exists in the address list.
 11. A protection switchingmethod of a share node connected to a share link having a failure in amulti-ring network, the protection switching method comprising:generating a protection switching frame for each ring; and transmittingthe protection switching frame to the each ring, wherein the protectionswitching frame comprises from among addresses of a forwarding table ofthe share node: an address corresponding to a port connected to theshare link while belonging to a ring that is to transmit the protectionswitching frame; and an address corresponding to a blocked port in aneighboring ring direction while belonging to a neighboring ring insteadof the ring that is to transmit the protection switching frame.
 12. Theprotection switching method of claim 11, wherein the transmittingcomprises transmitting the protection switching frame to the each ringvia a port that exists at opposite direction of the share link.
 13. Theprotection switching method of claim 11, further comprising the sharenode blocking a bridge connecting two rings.
 14. The protectionswitching method of claim 9, further comprising the share noderecognizing addresses of the forwarding table corresponding to the portconnected to the share link, and changing a port number of therecognized addresses to a port number of a ring to which the recognizedaddresses belong from among port numbers connected to each ring andexisting in an opposite direction of the share link.
 15. The protectionswitching method of claim 11, wherein, when the multi-ring network is anEthernet, each ring is classified by a virtual local area network (VLAN)identification (ID).
 16. The protection switching method of claim 11,wherein each ring is classified by a virtual private network (VPN)assigned number in the multi-ring network.
 17. The protection switchingmethod of claim 11, wherein, when the multi-ring network is a labelswitching network, each ring is classified by a multicast label.